R: Loop to create new data frames in R - r

Question

I am trying to create a loop which creates a number of files for a VCS Station that are named according to their station name. Below is the code that does this for one station, and I am trying to turn it into a loop so I can do it for 68 stations. (i.e. if I was copying and pasting I would be replacing the P205187 with a different station name, say P205200). I have the individual station names (e.g. P205187) in a dataframe called VCS.Sites. Can anyone point me in the right direction? New R user here and I am stuck!
P205187 <- VCSrawdata[VCSrawdata$Network_ID=="P205187",] #create a file for VCS station P205187
#clean up after subset
P205187$Network_ID <- factor(P205187$Network_ID)
# create annual file for VCS station P205187
P205187_annual <- group_by(P205187,Year,DESCRIPTION)
P205187_annual <- summarise(P205187_annual,Sum_Annual = sum(Value), Mean_Annual = mean(Value), CountDays=n())
# create monthly file for VCS station P205187
P205187_monthly <- group_by(P205187,Year, Month,DESCRIPTION)
P205187_monthly <- summarise(P205187_monthly,Sum_Monthly = sum(Value),Mean_monthly = mean(Value),CountDays=n())

Answer 1

You could do it quite well with an lapply loop. Something like this:
list_of_ids <- c("List be here")
monthly <- function(id){
P205187 <- VCSrawdata[VCSrawdata$Network_ID==id,] #create a file for VCS station P205187
#clean up after subset
P205187$Network_ID <- factor(P205187$Network_ID)
# create annual file for VCS station P205187
P205187_annual <- group_by(P205187,Year,DESCRIPTION)
P205187_annual <- summarise(P205187_annual,Sum_Annual = sum(Value), Mean_Annual = mean(Value), CountDays=n())
# create monthly file for VCS station P205187
P205187_monthly <- group_by(P205187,Year, Month,DESCRIPTION)
P205187_monthly <- summarise(P205187_monthly,Sum_Monthly = sum(Value),Mean_monthly = mean(Value),CountDays=n())
return(P205187_monthly)
}
monthlies <- lapply(list_of_ids, monthly)

Answer 2

It sounds like this is for writing csvs. We can use group_map from dplyr to loop through all of the stations and write csvs.
library(dplyr)
VCSrawdata %>%
group_by(Network_ID) %>%
group_walk(~ {
.x%>%
group_by(Year, DESCRIPTION) %>%
summarize(sum_annual = sum(Value),
mean_annual = mean(Value),
countDays = n())%>%
write.csv(file = paste0(.y$Network_ID, "_annual_csv"))
.x%>%
group_by(Year, Month, DESCRIPTION) %>%
summarize(sum_month = sum(Value),
mean_month = mean(Value),
countDays = n())%>%
write.csv(file = paste0(.y$Network_ID, "_month_csv"))
}
)
Things to note:
The .x is referring to the the grouped tibble that is split by Network_ID
The .y is referring to the grouping. In this case, we only have Network_ID.

Answer 3

Simply generalize your process in a defined method, then pass station names as a parameter in a loop or apply function to iterate through stations. With this approach you avoid many separate objects flooding global environment and instead use a single named list of many underlying elements for better serialization and organization.
summarize_stations <- function(station_name) {
tmp_df <- VCSrawdata[VCSrawdata$Network_ID==station_name,]
tmp_df$Network_ID <- factor(tmp_df$Network_ID)
# create annual file for VCS station
tmp_annual <- summarise(group_by(tmp,Year,DESCRIPTION),
Sum_Annual = sum(Value),
Mean_Annual = mean(Value),
CountDays=n())
# create monthly file for VCS station
tmp_monthly <- summarise(group_by(tmp, Year, Month,DESCRIPTION),
Sum_Annual = sum(Value),
Mean_Annual = mean(Value),
CountDays=n())
# RETURN NAMED LIST OF BOTH AGGREGATIONS
return(list(annual=tmp_annual, monthly=tmp_monthly))
}
station_list <- sapply(VCS.Sites$station_names, summarize_stations, simplify=FALSE)
# ACCESS UNDERLYING ELEMENTS
station_list$P205187$annual
station_list$P205187$monthly
...
You can even use by (object-oriented wrapper to tapply) to subset VCSrawdata by Network_ID (assuming it includes all your needed stations). To do so, slightly adjust function to receive a data frame as parameter which allows you to skip subset line.
summarize_stations <- function(tmp_df) {
# REMOVE SUBSET LINE
# tmp_df <- VCSrawdata[VCSrawdata$Network_ID=="P205187",]
...keep same code as above
}
station_list <- by(VCSrawdata, VCSrawdata$Network_ID, FUN=summarize_stations)
# ACCESS UNDERLYING ELEMENTS
station_list$P205187$annual
station_list$P205187$monthly
...